A new experiment conducted by psychologists at the University of California, Berkeley, shows that memory and language are in fact deeply linked, via the hippocampus, which plays a key role in memory associations.
The hippocampus, nestled in the center of the brain, acts like a router to link related memories - the color, shape, feel, scent and taste of an orange, for example - so that we are able to make associations. And its role in relating incoming words to stored semantic knowledge, according to the researchers in a paper published on Monday in the early online edition of the journal Proceedings of the National Academy of Sciences, is necessary in understanding and generating sentence meaning
"The link between language and the hippocampus could be an explanation for some of the language deficits we see in patients who don' t have damage to the language areas of the brain," former UC Berkeley postdoctoral fellow Vitória Piai, now a senior researcher at Radboud University in Nijmegen, the Netherlands, was quoted as saying by a UC Berkeley news release. "I think that once we start studying language as it happens in real life, we will find that the hippocampus is doing more in the service of language than we thought before."
The researchers recorded neuronal activity using electrodes inserted into the hippocampus of 12 people as they heard fill-in-the-blank sentences with an obvious answer. In most of the subjects, the hippocampus showed highly synchronized activity as they homed in on the right answer while hearing the sentences but before a picture of the answer was displayed, a sign that the region was making associations throughout the brain to come up with the right word: in this case, broom.
The study was conducted in epilepsy patients undergoing intracranial electrode studies at two medical institutions to locate the source of their abnormal brain activity. Piai recorded only from the non-epileptic hemisphere of the brain. In 10 of the 12 subjects, only constrained sentences, or those with a single obvious answer, caused a burst of synchronized theta waves in the hippocampus, activity characteristic of the hippocampus when it makes a memory association.
"Vitória showed that when you record directly from the human hippocampal region, as the sentence becomes more constraining, the hippocampus becomes more active, basically predicting what is going to happen," said Robert Knight, a UC Berkeley professor of psychology and former head of the Helen Wills Neuroscience Institute. "The hippocampus started building up rhythmic theta activity that is linked to memory access and memory processing."
"Language is something that has classically been viewed as evolving and occurring in the cortex, which is why we have language and rats don't," he noted. "Despite the fact that the hippocampal area of the medial part of the temporal lobe is well known to be linked to spatial and verbal memory in humans, the two fields have been like ships running in the fog, unaware that the other ship is there."
The new findings could open up a whole new area of study with intracranial recordings to probe details of the connection between language and memory, Knight said, adding that "this study shows that memory contributes as a sentence is evolving in time; it is a real-time part of our language system, not a slave to the language system."
